It is known to arrange for flow of coolant liquid within a cavity formed either in the casing of the alternator or in a bearing of the alternator, so as to cool the latter effectively. This enables both the power output and the compactness of such a machine to be improved. In addition, as compared with cooling by air ventilation, the cooling of the machine by use of a liquid is significantly more silent.
The use of a liquid cooling circuit for the alternator is therefore of particular relevance in the context of the current tendency for continuously increasing the demand for electrical energy in motor vehicles, which is due to the steady increase in the number of auxiliary items of equipment that have electric motors. This increase in the demand for current to be produced by the alternator leads to a need for corresponding adaptation of the current regulating means, and particularly of a means whereby the three-phase alternating current produced by the alternator is rectified, into a direct current, which can be stored in a battery of the vehicle or be used directly by the electrical circuit of the vehicle which is supplied with a direct-current voltage.
Rectification of the three-phase alternating current is generally obtained by means of a rectifier bridge having six power diodes. Three of these diodes are the positive diodes, and are connected between the outlets of the stator windings of the alternator and the positive terminal B+ of the alternator which is connected to the battery and the electrical circuit of the vehicle. Three further diodes, namely the negative diodes, are connected between electrical ground or earth of the vehicle and the input side of the stator windings.
The diodes which nowadays constitute the rectifier bridge are subjected to high current intensities. Hence, it is necessary to cool them in the most effective way possible. To this end, it is known to arrange the diodes on metal plates, which are arranged on the outside of the alternator and which constitute a dissipator for the heat produced by the diodes. The diodes are accordingly grouped on two plates, one of which is reserved for the positive diodes, and the other for the negative diodes.
However, under certain particularly severe operating conditions, it has become apparent that this cooling of the diodes, and in general terms the cooling of the whole of the current regulating means, can be insufficient to ensure good performance of the alternator.